1. Field of the Invention
The present invention generally relates to creating and viewing virtual microscope slide images and more particularly relates to the creating and viewing of three dimensional virtual microscope slide images.
2. Related Art
Conventional microscopes, using mechanical focusing mechanisms of sufficient quality, are easily focused by an observer. The feedback loop between the eye/brain and the fingers is extremely rapid and accurate. If any part of the feedback loop is impaired, however, the process of obtaining perfect focus becomes extremely difficult, time consuming and even inaccurate. These impairments may arise from poor optical quality, insufficient or incorrect illumination, inaccuracies in the focusing mechanism, or even due to poor visual acuity of the operator.
More recently, conventional computer implemented microscope systems have provided the ability to remotely access high resolution images of microscope slides for a number of years. Devices capable of creating such images fall into two broad categories: (1) remote controlled (or robotic) microscopes; and (2) imagers, which create some type of electronic or photographic image of some, or all, of the specimen. Each type has its advantages and disadvantages, many of which are unique to the particular application.
Remote controlled microscopes, which essentially replace the operator's eye with an electronic camera, allow the operator to control the focus plane of the camera. This capability is particularly advantageous when viewing thick specimens. However, the optical field of view at moderate or high resolution is extremely small due to a limited number of camera pixels. This makes it very difficult and time consuming to view an entire specimen on a microscope slide even at moderate magnification.
Conventional imaging systems are capable of creating large enough images to capture an entire specimen at moderate or high magnification. These images are called virtual microscope slides or virtual slides. Because of their extremely large size, virtual slides are usually limited to a single focus level (“Z-plane”). Many types of microscope specimens are very thin so a single Z-plane virtual slide is sufficient. Other types of microscope specimens, however, are thicker than the depth of field of the objective lens.
Remote controlled microscopes additionally suffer from an even more degrading effect—time lag. Because a remotely controlled microscope is merely a microscope with motorized stages for positioning and focusing the specimen, and a camera to transmit images to a remote user, if the image being displayed to the user is delayed by even a small fraction of a second, the feedback loop will be frustrating, if not nearly impossible to use. The user, viewing the electronic image on a remote monitor, will attempt to converge on the optimally focused image, only to find that the image continues to zoom after he has attempted to stop at the best focus. The process must then be repeated in smaller and smaller iterations, at slower and slower speeds until finally, a satisfactory focus is obtained. Time lag in conventional systems, in particular as it applies to a networked attached device making use of an internet connection, has several contributing causes. One cause can be traced to the design of the device itself. Poor system design, and inefficient data processing methods can add significantly to the perceived sluggishness of conventional systems.
Two other factors are more serious in that they cannot always be controlled by the designer. The first is bandwidth. Bandwidth refers to the capacity of a network to transmit data, or in the case of a robotic microscope, the imagery being displayed to the operator, and the control signals returning to the device to affect its position and focus. Low network bandwidth limits the update rate of the image on the video display. Fortunately, increased bandwidth may be purchased at greater expense, effectively solving this problem. The second problem, called latency, is not so easily solved. Latency is simply the delay time between network nodes. Even fast networks have some degree of latency. Delays, often on the order of seconds, are not uncommon over the Internet. Latency is the Achilles heel of real-time feedback control systems.
What is needed is a remote device that appears to the user as an extremely responsive, high bandwidth, low latency, remote controlled microscope that does not suffer from the limitations of the conventional systems described above.